A boy was slashed across the leg in an attack by "teenage boys roughly aged 13-15" in West Molesey.
Police responded at 7.50pm after the ambulance service reported the attack on Walton Road outside Sainsbury's on January 2.
The victim was taken to hospital where his injuries were confirmed as serious, but not life-threatening.
The suspect of the attack then fled the scene. Following this, a second suspect punched the victim and also fled.
Both suspects are described as boys aged roughly 13 to 15.
The first suspect wore a balaclava, while the second was identified as a white boy.
A 15-year-old boy has since been arrested on suspicion of affray and remains in police custody.
Borough commander inspector Bert Dean said: “This is understandably a shocking incident. Officers will be in the area conducting patrols and engaging with the community. I’d encourage you to speak with them if you have concerns.
“A teenage boy was arrested last night in connection with this attack and I’d urge anyone who has information that can help our investigation to please get in touch.”
Police are appealing to any witnesses of the assault, particularly those who were travelling on Walton Road between 7.30pm and 7.50pm and might have captured the incident on dashcam, to come forward.
For those who do not wish to speak with police, independent charity Crimestoppers can be contacted on 0800 555 111.
Tip-offs can also be submitted via webchat, an online reporting tool on Surrey Police's website, or by calling 101, quoting reference PR/45240000687.
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules here